It is expeditious and convenient in certain types of installations to utilize storage batteries as a source of power for operating various electrical devices, such as, lights, motors, relays, radio equipment or the like. It is essential to maintain the battery fully charged at all times so that sufficient electrical power is available during subsequent demands by the load. Thus, it is common practice to provide an appropriate battery charger for restoring the electrical energy that was depleted from the battery by the load. However, the battery charger should not overcharge the storage battery for extended periods of time since violent gassing occurs and the loss of electrolyte can cause irreparable damage or can result in reduced power capacity. Thus, it is essential that the charging rate should be controlled in accordance with the condition of the battery, namely, the voltage condition since the voltage is a function of the charge condition of the battery. It is apparent that when the battery reaches a fully charged condition, the charging current should be automatically cut-off in order to obtain maximum efficiency and to realize long battery life. However, when using a taper type of battery charging technique, it has been found to be a requisite to build into the battery charger, an overcharging or equalizing charging capability. When a fully charged battery has not been used for an extended period of time, it is generally necessary to provide an overcharging or equalizing charge in order to recondition the battery for meeting subsequent load demands. Accordingly, it is good preventative maintenance to periodically overcharge a dormant or seldom used battery at least once a month. The controlled overcharge is periodically given in order to keep the battery in a peak condition and to prevent the development of inequalities in the condition of the individual cells. Further, when replacing an expired battery, it is common practice to condition the new battery by overcharging it for a short period of time. In addition to the above-noted requirement, an acceptable battery charger must be capable of withstanding large transient voltages, short circuited output conditions and accidental reverse polarity connections without resultant damage or permanent failure.